Hot rolled strips, which are sequentially fed from a hot strip mill, are cooled while passing over a run-out table of the mill. In the above state, the process for cooling the hot rolled strips has typically been executed by spraying coolant from nozzles of a coolant header onto a hot rolled strip. Conventional coolant headers, which spray coolant onto hot rolled strips from nozzles, have been classified into turbulent flow-type headers, spray-type headers and laminar flow-type headers according to the coolant spraying style.
The turbulent flow-type coolant headers are configured such that high pressure is applied to the interior of a coolant header and coolant is sprayed onto a hot rolled strip. Thus, the turbulent flow-type headers necessarily have new devices to produce high pressure, thus having complex construction and increasing installation costs. Furthermore, the velocity of coolant sprayed from nozzles of the turbulent flow-type coolant header is very high, so that the flow of coolant which is sprayed from the nozzles and cools the hot rolled strips is unstable. Thus, when the turbulent flow-type coolant headers are used to cool hot rolled strips, large temperature deviations may be induced in each of the strips along the width of the strip.
On the contrary, the spray-type coolant headers to spray coolant through nozzles having small diameters may evenly spray coolant over the overall surface area of each hot rolled strip. However, the spray-type coolant headers are problematic in that the flow rate of coolant sprayed from a header per unit time is not too enough at normal pressure condition, so that the header cannot quickly cool the hot rolled strips and, furthermore, the strip cooling efficiency is reduced. Thus, it is not easy for the spray-type coolant headers to control the temperature of the strips while cooling the strips.
The laminar flow-type coolant headers solve the problems of the two above-mentioned types of coolant headers by discharging relatively stabilized coolant and by evenly cooling the hot rolled strips along the width of each strip.
FIG. 1 illustrates a sectional area of a conventional laminar flow-type coolant header having the above-mentioned properties.
As shown in FIG. 1, the conventional laminar flow-type coolant header comprises an outer tub 10 to store coolant therein, two inner tubs 20 to guide the coolant current discharged from the header onto the surface of a hot rolled strip, and a coolant supply pipe 30 to supply the coolant to the outer tub 10. In the coolant header, both the inner tubs 20 and the coolant supply pipe 30 are arranged along the width of the hot rolled strip.
The coolant supply pipe 30 is arranged between the two inner tubs 20 which are arranged in two lines, with two coolant outlet holes 31 formed on an end of the coolant supply pipe 30 so as to supply the coolant to the respective inner tubs 20. However, when the coolant discharged from the outlet holes 31 is directly introduced into the inner tubs 20, the coolant may flow undesirably quickly and become unstable. Thus, to allow the outlet coolant to flow stably, the outlet holes 31 are placed lower than the inlet holes of the inner tubs 20. Furthermore, to cause the coolant to reliably flow in the laminar flow pattern, both a perforated plate 40 and a flow stabilizing filter 50 are placed in a path through which the coolant flows to each inner tub 20. Therefore, the coolant, finally discharged from the inner tubs 20 through discharging holes 21, flows in a very stable flow pattern.
However, the conventional laminar flow-type coolant header having the above-mentioned construction is problematic in that, because the header has only two rows of discharging holes 21 in a single outer tub 10, the header may not discharge a large amount of coolant onto a hot rolled strip at one time, thus failing to provide a high cooling rate. Therefore, to quickly cool a hot rolled strip having a high temperature using the conventional laminar flow-type coolant headers, a great number of coolant headers must be coupled together in series, thus enlarging the size of a hot rolled strip cooling device and increasing the installation costs of the device.